The invention relates to a run flat pneumatic tire utilizing reinforcing wedges of different hardness in the tire sidewall.
The basic concept of run flat tires has been around for many years. Many of the early inventions, such as U.S. Pat. No. 4,130,154 (1978) used separate support members that were applied to the wheel rim. These support members provided a secondary device to support the tire in an uninflated condition. Advancements in rubber compounding technology, as well as tire building techniques, have made it possible to incorporate the uninflated support capabilities into the tire sidewall itself. This provides for a more practical solution to the run flat engineering problem due to a reduction in complexity. One of the early patents that utilized this approach was U.S. Pat. No. 4,193,437 (1980). This concept used an insert of rubber material in the tire sidewall that provided the necessary extra support to allow the tire to run without inflation. Many patents have since been issued to various companies that are all modifications of this same basic approach. Some examples include U.S. patents:
U.S. Pat. No. 4,405,007 (1983) U.S. Pat. No. 5,368,082 (1994), and U.S. Pat. No. 5,639,320 (1997) to Goodyear,
U.S. Pat. No. 5,427,166 (1995), U.S. Pat. No. 5,511,599 (1996), and U.S. Pat. No. 5,868,190 (1999) to Michelin,
U.S. Pat. No. 4,779,658 (1988), U.S. Pat. No. 4,917,164 (1990), U.S. Pat. No. 5,217,549 (1993), U.S. Pat. No. 5,427,176 (1995), and U.S. Pat. No. 5,529,105 (1996) to Firestone.
These patents generally use different construction and compound techniques to reach the goal of good run flat performance. However, one feature they all have in common is that they use sidewall inserts that essentially extend substantially the full radial sidewall length. This approach places a very difficult set of engineering requirements on one piece of material. Such material must provide adequate support and heat resistance performance for the entire sidewall height. Different zones in the sidewall have different performance characteristics. The upper sidewall region for instance is subjected to high flex and heat resistance requirements in the uninflated state. The lower sidewall zone, however, is subjected to much less stress. Moreover, the use of inserts that extend the full width of the sidewall makes it very difficult to balance tire performance characteristics.
A different concept is used in U.S. Pat. No. 5,309,970 (1994) which utilizes 3 specific sidewall zones. A relatively wide first reinforcing rubber insert transitions to a narrower second reinforcing insert which then transitions to the bead filler.
The characteristics of the above concepts are different from the proposed invention. Such concepts use the softest rubber compound in the upper sidewall region. The next hardest compound is the second reinforcing insert with the bead filler being the hardest compound. This approach has concentrated the stress on the upper first reinforcing insert instead of distributing it throughout the sidewall.
Another concept is set forth in U.S. Pat. No. 5,439,041 (1995) wherein the sidewall contains 3 basic zones. The upper zone in this case does not have any reinforcing insert. The middle section of the sidewall is reinforced with a xe2x80x9celastomeric spongexe2x80x9d type insert with the lower third consisting of a sandwich of this sponge and the bead filler. This concept also concentrates stresses in the upper sidewall region of the tire.
A final concept is set forth in U.S. Pat. No. 5,526,862 (1996) wherein reinforcement does not extend the full length of the sidewall. The inserts are graduated in hardness laterally across the sidewall cross section. The hardest insert is placed in the inner portion of the tire sidewall and makes up a small percentage of the total sidewall height. It is designed for the tire to collapse around this insert in the uninflated state. This concentrates stress in the mid sidewall region of the tire.
The present invention relates to a pneumatic run flat tire, which has a sidewall hardness profile or gradient, which generally, gradually decreases in a radial inward direction from the crown of the tire to the lower sidewall region. The gradient is obtained by utilizing a plurality of reinforcing wedges of different hardness, with the hardest wedge located in the radially outermost position. The hardness of the various wedges can be controlled by utilizing different compounding formulations. The shape, geometry, etc. of the wedges is such that generally a gradual change in hardness is obtained in going in either a radial inward or outward direction from a point defined by the thickest section width of the lower sidewall wedge. The result is a a more even stress distribution which allows for increased run flat performance while at the same time providing better tuning capabilities for other tire performance characteristics such as vehicle ride.